Add custom sslcontext support in fili

[Chandrasekar-Rajasekar]

User must override getSSLContext method to give their own sslContext. The function should return the object of io.netty.handler.ssl.SslContext.

protected SslContext getSSLContext() {
        //create SSL Context here
       if(sslContext.instanceOf(io.netty.handler.ssl.SslContext.class)) 
              return sslContext;
       if(sslContext.instanceOf(javax.net.ssl.SSLContext.class))
              return new JdkSslContext(sslContext, true, ClientAuth.REQUIRE)
      .
      .
      .
      return null
}

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[michael-mclawhorn]

definitely need a change to CHANGELOG, and you should probably create an issue to link to in the changelog ticket.

Should also add a test to config that this code gets excercised.